process-warn-on-exit: preference variable

Default value: 0

If this variable is set to 1, whenever you try to exit Epsilon and
a concurrent process is running (or there's a connected telnet or ssh
buffer), Epsilon will use the exit-process command to try to make
it exit. If the process refuses to exit, Epsilon will display an
error message, and won't exit. If this variable is set to 2 and
there's a running process or a connected telnet or ssh buffer, Epsilon
will prompt for permission to exit, but it won't use exit-process.